The present application is based on Japanese Patent Application No. 10-337697 filed Nov. 27, 1998, the contents of which are incorporated hereinto by reference.
1. Field of the Invention
The present invention relates to a blood pressure monitor apparatus which monitors a blood pressure of a living subject based on pulse-wave-propagation-velocity-relating information which relates to a propagation velocity of a pulse wave which propagates through an artery of a subject, pulse-period-relating information which relates to a period of a pulse of a subject, and peripheral-blood-volume-relating information which relates to a volume of blood which flows in a peripheral body portion of a subject.
2. Discussion of the Related Art
As pulse-wave-propagation-velocity-relating information, there is known a propagation time DT during which a pulse wave propagates between predetermined two portions of an artery, or a propagation velocity VM (m/s) at which a pulse wave propagates through an artery. It is generally known that such pulse-wave-propagation-velocity-relating information is substantially proportional to a blood pressure BP (mmHg) of a living subject within a predetermined range. In view of this, there is proposed a blood pressure monitor apparatus which monitors a change or fluctuation of the blood pressure of the subject by monitoring whether or not successively obtained pulse-wave-propagation-velocity-relating information is greater than a predetermined upper reference value or smaller than a predetermined lower reference value, and judges that the blood pressure has changed and starts a blood pressure measurement using a cuff when the obtained pulse-wave-propagation-velocity-relating information is greater than the predetermined upper reference value or smaller than the predetermined lower reference value.
However, the pulse-wave-propagation-velocity-relating information is not proportional to the blood pressure in an entire blood pressure range. Namely, the correlation between the pulse-wave-propagation-velocity-relating information and the blood pressure is considerably low in a considerably low blood pressure range and a considerably high blood pressure range. Accordingly, the conventional blood pressure monitor apparatus which monitors the change of the blood pressure based on the pulse-wave-propagation-velocity-relating information is not capable of accurately detecting the change of the blood pressure in the entire blood pressure range.
It is therefore an object of the present invention to provide a blood pressure monitor apparatus which is capable of accurately detecting a change or fluctuation of the blood pressure of a living subject in the entire blood pressure range.
As a result of an extensive study by the inventors of the present invention, it has been found that the change of the blood pressure can be detected with high accuracy in the entire blood pressure range if other information which is correlative with the blood pressure is used to monitor the blood pressure, in addition to the pulse-wave-propagation-velocity-relating information. Such information includes pulse-period-relating information which relates to a period of a pulse of the subject, such as a pulse period and a heart rate, and peripheral-blood-volume-relating information which relates to a volume of blood flowing in a peripheral body portion of the subject, such as an amplitude and an area of a pulse wave detected from the peripheral body portion of the subject.
The above-indicated object of the present invention may be attained according to a principle of the invention, which provides a blood pressure monitor apparatus for monitoring a blood pressure of a living subject, comprising: pulse-wave-propagation-velocity-relating information obtaining means for successively obtaining pulse-wave-propagation-velocity-relating information which relates to a pulse-wave propagation velocity at which a pulse wave propagates in an artery of the subject; pulse-period-relating information obtaining means for successively obtaining pulse-period-relating information which relates to a pulse period of the subject; peripheral-blood-volume-relating information obtaining means for successively obtaining peripheral-blood-volume-relating information which relates to a volume of blood which flows in a peripheral body portion of the subject; and abnormality judging means for judging that the blood pressure of the subject is abnormal when at least one of the pulse-wave-propagation-velocity-relating information, pulse-period-relating information, and peripheral-blood-volume-relating information does not fall within a corresponding one of a first, a second and a third reference range.
In the blood pressure monitor apparatus constructed as described above, the change of the blood pressure of the subject can be detected with high accuracy in the entire blood pressure range since the blood pressure of the subject is judged to be abnormal when at least one of the pulse-period-relating information and the peripheral-blood-volume-relating information does not fall within a corresponding one of the second and third reference ranges, even if the pulse-wave-propagation-velocity-relating information may fall within the corresponding first reference range.
In a preferred form of the present invention, the first, second, and third reference ranges have a first, a second, and a third upper limit value, respectively. The first, second, and third reference ranges may or may not have a lower limit value.
In a preferred form of the present invention, the first, second, and third reference ranges have a first, a second, and a third lower limit value, respectively. The first, second, and third reference ranges may or may not have an upper limit value.
In a preferred form of the present invention, the first, second, and third reference ranges have a first, a second, and a third upper limit value, respectively, and a first, a second, and a third lower limit value, respectively.
In a preferred form of the present invention, the first, second, and third upper limit values are a common value. The first, second, and third upper limit values may be different from one another.
In a preferred form of the present invention, the first, second, and third lower limit values are a common value. The first, second, and third lower limit values may be different from one another.
In a preferred form of the present invention, the blood pressure monitor apparatus further comprises blood pressure measuring means which includes a cuff and which measures a blood pressure of the subject by changing a pressing pressure of the cuff applied to a body portion of the subject, and the abnormality judging means starts a blood pressure measurement of the blood pressure measuring means when the blood pressure of the subject is judged to be abnormal.
The blood pressure monitor apparatus constructed according to the above arrangement starts the blood pressure measurement of the blood pressure measuring means when at least one of the pulse-period-relating information and the peripheral-blood-volume-relating information does not fall within a corresponding one of the second and third reference ranges, even if the pulse-wave-propagation-velocity-relating information may fall within the corresponding first reference range. Accordingly, the present blood pressure monitor apparatus is capable of quickly obtaining the blood pressure of the subject with high reliability in the entire blood pressure range when the blood pressure of the subject has changed.
In a preferred form of the present invention, the pulse-wave-propagation-velocity-relating information obtaining means comprises first estimated blood pressure determining means for successively determining, as the pulse-wave-propagation-velocity-relating information, a first estimated blood pressure value EBP1, based on a pulse-wave propagation time, by utilizing a predetermined relationship between first estimated blood pressure value EBP1 and pulse-wave propagation time DTRP, the relationship being represented by an equation:EBP1=xcex11(1/DTRP)+xcex21, wherein xcex11 and xcex21 represent coefficients, the pulse-period-relating information obtaining means comprises second estimated blood pressure determining means for successively determining, as the pulse-period-relating information, a second estimated blood pressure value EBP2, based on a pulse period of the subject, by utilizing a predetermined relationship between second estimated blood pressure value EBP2 and pulse period RR, the relationship being represented by an equation:EBP2=xcex12RR+xcex22, wherein xcex12 and xcex22 represent coefficients, and the peripheral-blood-volume-relating information obtaining means comprises third estimated blood pressure determining means for successively determining, as the peripheral-blood-volume-relating information, a third estimated blood pressure value EBP3, based on a pulse-wave area, by utilizing a predetermined relationship between third estimated blood pressure value EBP3 and pulse-wave area VR, the relationship being represented by an equation:EBP3=xcex13VR+xcex23, wherein xcex13 and xcex23 represent coefficients.
In a preferred form of the present invention, pulse-wave-propagation-velocity-relating information obtaining means comprises an electrocardiographic-waveform detecting device which includes a plurality of electrodes adapted to be attached to a body portion of the subject and detects an electrocardiographic waveform indicative of an action potential of a cardiac muscle of the subject through the electrodes, and a photoelectric-pulse-wave detecting device which includes a plurality of light-emitting elements and a light-receiving element, each of the light-emitting elements emitting, toward a body surface of the subject, a light having a wavelength which is reflected by hemoglobin present in the blood of the subject, the light-receiving element receiving the light scattered by the hemoglobin from the body surface of the subject, the photoelectric-pulse-wave detecting device detecting a photoelectric pulse wave indicative of the volume of the blood flowing in the body surface, the pulse-wave propagation time (DTRP) representing a time difference between a predetermined point of a pulse of the electrocardiographic waveform detected by the electrocardiographic-waveform detecting device, and a predetermined point of a waveform of a corresponding pulse of the photoelectric pulse wave detected by the photoelectric-pulse-wave detecting device.
In a preferred form of the present invention, the pulse-period-relating information obtaining means comprises an electrocardiographic-waveform detecting device which includes a plurality of electrodes adapted to be attached to a body portion of the subject and detects an electrocardiographic waveform indicative of an action potential of a cardiac muscle of the subject through the electrodes, the pulse period (RR) representing an interval between successive two R-waves of the electrocardiographic waveform detected by the electrocardiographic-waveform detecting device.
In a preferred form of the present invention, the peripheral-blood-volume-relating information obtaining means comprises a photoelectric-pulse-wave detecting device which includes a plurality of light-emitting elements and a light-receiving element, each of the light-emitting elements emitting, toward a body surface of the subject, a light having a wavelength which is reflected by hemoglobin present in the blood of the subject, the light-receiving element receiving the light scattered by the hemoglobin from the body surface of the subject, the photoelectric-pulse-wave detecting device detecting a photoelectric pulse wave indicative of the volume of the blood flowing in the body surface, the pulse-wave area (VR) representing an area defined by a waveform of a pulse of the photoelectric pulse wave detected by the photoelectric-pulse-wave detecting device.